Android架构组件Room的使用详解

allprojects {
  repositories {
    jcenter()
    google()
  }
}

dependencies {
  // Room
  implementation "android.arch.persistence.room:runtime:1.0.0"
  annotationProcessor "android.arch.persistence.room:compiler:1.0.0"
}

@Entity(tableName = "tb_class")
public class ClassEntity {
  @PrimaryKey
  private long id;
}

//指示数据表实体类
@Entity(tableName = "tb_student",//定义表名
    indices = @Index(value = {"name", "sex"}, unique = true),//定义索引
    foreignKeys = {@ForeignKey(entity = ClassEntity.class,
        parentColumns = "id",
        childColumns = "class_id")})//定义外键
public class StudentEntity {
  @PrimaryKey //定义主键
  private long id;
  @ColumnInfo(name = "name")//定义数据表中的字段名
  private String name;
  @ColumnInfo(name = "sex")
  private int sex;
  @Ignore//指示Room需要忽略的字段或方法
  private String ignoreText;
  @ColumnInfo(name = "class_id")
  private String class_id;
  //setter and getter
}

public @interface Entity {
 //定义表名
  String tableName() default "";
 //定义索引
  Index[] indices() default {};
 //设为true则父类的索引会自动被当前类继承
  boolean inheritSuperIndices() default false;
 //定义主键
  String[] primaryKeys() default {};
 //定义外键
  ForeignKey[] foreignKeys() default {};
}

public @interface Index {
 //定义需要添加索引的字段
 String[] value();
 //定义索引的名称
 String name() default "";
 //true-设置唯一键，标识value数组中的索引字段必须是唯一的，不可重复
 boolean unique() default false;
}

public @interface ForeignKey {
 //引用外键的表的实体
 Class entity();
 //要引用的外键列
 String[] parentColumns();
 //要关联的列
 String[] childColumns();
 //当父类实体(关联的外键表)从数据库中删除时执行的操作
 @Action int onDelete() default NO_ACTION;
 //当父类实体(关联的外键表)更新时执行的操作
 @Action int onUpdate() default NO_ACTION;
 //在事务完成之前，是否应该推迟外键约束
 boolean deferred() default false;
 //给onDelete，onUpdate定义的操作
 int NO_ACTION = 1;
 int RESTRICT = 2;
 int SET_NULL = 3;
 int SET_DEFAULT = 4;
 int CASCADE = 5;
 @IntDef({NO_ACTION, RESTRICT, SET_NULL, SET_DEFAULT, CASCADE})
 @interface Action {
  }
}

@Dao
public interface StudentDao {
  @Query("SELECT * FROM StudentEntity")
  List getAll();
  @Query("SELECT * FROM StudentEntity WHERE id IN (:ids)")
  List getAllByIds(long[] ids);
  @Insert
  void insert(StudentEntity... entities);
  @Delete
  void delete(StudentEntity entity);
  @Update
  void update(StudentEntity entity);
}

public @interface Insert {
  //定义处理冲突的操作
  @OnConflictStrategy 
  int onConflict() default OnConflictStrategy.ABORT;
}
public @interface OnConflictStrategy {
  //策略冲突就替换旧数据
  int REPLACE = 1;
  //策略冲突就回滚事务
  int ROLLBACK = 2;
  //策略冲突就退出事务
  int ABORT = 3;
  //策略冲突就使事务失败 
  int FAIL = 4;
  //忽略冲突
  int IGNORE = 5;
}

@Database(entities = {StudentEntity.class}, version = 1)
public abstract class RoomDemoDatabase extends RoomDatabase {
  public abstract StudentDao studentDao();
}

RoomDemoDatabase database = Room.databaseBuilder(getApplicationContext(),       RoomDemoDatabase.class, "database_name")
        .build();

Room.databaseBuilder(getApplicationContext(),
            RoomDemoDatabase.class, "database_name")
            .addCallback(new RoomDatabase.Callback() {
              //第一次创建数据库时调用，但是在创建所有表之后调用的
              @Override
              public void onCreate(@NonNull SupportSQLiteDatabase db) {
                super.onCreate(db);
              }

              //当数据库被打开时调用
              @Override
              public void onOpen(@NonNull SupportSQLiteDatabase db) {
                super.onOpen(db);
              }
            })
            .allowMainThreadQueries()//允许在主线程查询数据
            .addMigrations()//迁移数据库使用，下面会单独拿出来讲
            .fallbackToDestructiveMigration()//迁移数据库如果发生错误，将会重新创建数据库，而不是发生崩溃
            .build();

Room.databaseBuilder(getApplicationContext(), MyDb.class, "database-name")
    .addMigrations(MIGRATION_1_2, MIGRATION_2_3).build();

static final Migration MIGRATION_1_2 = new Migration(1, 2) {
  @Override
  public void migrate(SupportSQLiteDatabase database) {
    database.execSQL("CREATE TABLE `Fruit` (`id` INTEGER, "
        + "`name` TEXT, PRIMARY KEY(`id`))");
  }
};
static final Migration MIGRATION_2_3 = new Migration(2, 3) {
  @Override
  public void migrate(SupportSQLiteDatabase database) {
    database.execSQL("ALTER TABLE Book "
        + " ADD COLUMN pub_year INTEGER");
  }
};

class Address {
  public String street;
  public String state;
  public String city;
  @ColumnInfo(name = "post_code")
  public int postCode;
}
@Entity
class User {
  @PrimaryKey
  public int id;
  public String firstName;
  @Embedded
  public Address address;
}

 @Embedded(prefix = "foo_")
 Coordinates coordinates;

// ReactiveStreams support for LiveData
implementation "android.arch.lifecycle:reactivestreams:1.0.0"

@Dao
public interface MyDao {
  @Query("SELECT first_name, last_name FROM user WHERE region IN (:regions)")
  public LiveData> loadUsersFromRegionsSync(List regions);
}

// RxJava support for Room
implementation "android.arch.persistence.room:rxjava2:1.0.0"

@Dao
public interface MyDao {
  @Query("SELECT * from user where id = :id LIMIT 1")
  public Flowable loadUserById(int id);
}

@Dao
public interface MyDao {
  @Query("SELECT * FROM user WHERE age > :minAge LIMIT 5")
  public Cursor loadRawUsersOlderThan(int minAge);
}

public class Converters {
  @TypeConverter
  public static Date fromTimestamp(Long value) {
    return value == null &＃63; null : new Date(value);
  }
  @TypeConverter
  public static Long dateToTimestamp(Date date) {
    return date == null &＃63; null : date.getTime();
  }
}

@Database(entities = {User.class}, version = 1)
@TypeConverters({Converters.class})
public abstract class AppDatabase extends RoomDatabase {
  public abstract UserDao userDao();
}

@Entity
public class User {
  ...
  private Date birthday;
}
@Dao
public interface UserDao {
  ...
  @Query("SELECT * FROM user WHERE birthday BETWEEN :from AND :to")
  List findUsersBornBetweenDates(Date from, Date to);
}

build.gradle
android {
  ...
  defaultConfig {
    ...
    javaCompileOptions {
      annotationProcessorOptions {
        arguments = ["room.schemaLocation":
               "$projectDir/schemas".toString()]
      }
    }
  }
}